Ice detector



P198212 XR 2,359,787

250-201 AU 252 EX in HAMMER Oct. 10, 1944. ERS HAL 2,359,787

ICE DETECTOR Filed Jan. 21, 1942 new use 16, i944 Ielville F.

Garrett Park, ton. Ohio ICE nmc'roa mm. Beltsviile, and John 1. m

Md, and Hem-1M. Taylor, Day- Application January 21.342, Serial m. 4mmClaims- (Cl. m-su) (Granted nnder the m of March amended April 80, 1928:370 O. G. 157) Our invention to apparatus for detecting the formation ofice upon a surface. The

invention has particular utility when applied to aircraft where we isquite common and dangerone, often bringing about a termination offlight.

Ice may form upon an airfoil surface, particularlythe leading edges ofawing. Itmayalso form upon the interior surface of the air intake ductof the carburetor of an aircraft engine which is likewise verydangerous, often freezing the carburetor throttling mechanism.

It is therefore a broad object of our invention to provide an improvedapparatus for detecting when ice begins to form on a surface sothatasignal can be given and/or any deicing mechanism canbeautomatically set'into operation.

A specific object of our invention is to proice upon a surface, whichincludes a prism-like light pervious member such as glass having oneface exposed flush with the surface. A ray of light projected into thelight pervious member so that it will strike the exposed face at anangle greater than the critical angle for the medium is totallyreflected into a light sensitive device, but only in the event that theface is free from ice, thus providing fora change in light to bereceived by the light sensitive device. and which change may be utilisedto operate an ice indicator and/or control the operation of any de-icingmechanism which may have been provided.

and other obiects of our invention will 'niese become more apparent fromthe following -descripticn and drawing vide an apparatus for detectingthe presence of ice upon a surface, the primary elements of theapparatus comprising a light sensitive deviceandasourceoflightraystherefor,theraysbe-- ing subject to a displacementfrom their normal position relative to the light sensitive device as iceforms upon the surface to change the amount of light received by thelight sensitive device and thereby eii'ect operation of the detectingmeans.

Another object of our invention is to provide an apparatus fol-detectingthe presence of ice utilislngalightsensitivedeviceandasourceofiightraystherefor,theraysbeingdirectedintoalightperviousmemberandthencetothelight sensitive device relative towhich the rays are displacedupontheformationofioeuponafaceofthelightperviousmembertotherebychangetheamountofiightreceiv'edbythelightserisl--' tivedeviceandwhichchangeinlightisefiec-j tivetocamedetectingmeanssuchasanindica--'r tor or control device for initiating operation ofniitableiceremovalapparatustooperate.

totally. reflected from an exposedfaceofthelightperviousmemberintothelight sensitive devicewhenthereisnoice present onthefacebutbeingawayfromthe invention is to provide A For of illustration, which in noway is intended as a limitation ofthe claims appended hereto. oneembodiment of our invention is shown in the accompanying drawings anddescribed herewith with respect to its application to an airfoil surfaceofthedrawingJikepartsaredesignatedby like reference characters.

Referring now to the drawing: Fig. 1 isa diagramillustratlng thephenomenon 'of total reflection of light which is utilized in thepresent embodiment of our invention.

Fig. 2 is a sectional view in ing how our detecting apparatus in anairfoil; and

Pig. 3 is a detecting parts of our invention illustrated in 1"ig. 2,together with a suitable electric circuit for connecting the parts foroperation.

Referring to rig. 1. it is well known that when a ray of light so isfrom one light pervious medium to another, the ray-willbehenattheboundary'x -x' between the two mediums, becoming as. Thisphenomenon of light is knownas refraction. If, however, a ray of lightio'strikes the boundary between the two mediums at an angle to anormalYY' drawnbetweenthemediums atogreater thanacriticalanglek,theraywillnotpasson through but will be reflected of back intothe medium. This enon is sometimes referrred to as total reflection" andthe critical m I,

maybeinserted the light ray in the less refractive medium and I6 r'bethe angle ofthe light ray in the more of an aircraft. In the variousviews perspective showtic representation of the caused to pass atanangle which varies in accordance with the parfractive medium. theratiolof the sines of such angles,

sin 1' sin 1' 'isaconstantwhichmaybetermedn. IfarayNorayoflightstrikingtheboundaryatanangle greater than k, It being thecritical angle, can

'-emerge but will be totally reflected. For example, as between ice andair, the critical angle, Id is 48 36'. For crown glass and air, I: is 432.

Referring now to Fig. 2. we provide a light. pervious member I which isarranged so that one face 0. thereof is substantially flush with the topsurface of the airfoil 2. Face of member I, which is prismlike, shouldobviously have a contour corresponding to the contour of the particularsection of the airfoil in which it is situated in orderto eliminatedrag. Member I maybemade of any suitable material which will transmitlight, such as, for example, crown glass. The other two faces I: and cof member I are preferably plane surfaces arranged at right angles toeach other.

A light source I is suitably supported within a housing 4 interior-1y ofthe airfoil l and a beam of light therefrom is projected through lens Iinto member I andnormaltoface b. Sincefacesb and care atrightanglestoeachotherand beam of light enters member I normal to face b. the saidbeam of light will strike face 0 thereof at an angle of 45 to anormal toa tangent at the pointoonfaceaatwhichthebeamoflight impinges. Since thecritical angle for crown glassislessthan45,thebeamoflightwillnot passfrom member I at face a thereof but will be reflected thereby.

This reflection of the beam of light reflected from face a of the glassmember I, is caught by a photoelectric cell I which is suitablysupported in housing I. Housing I is provided with arelativelysmallopeninglthereininorderthatthe CROSS R EERENCE will strikea face a oflight'pervious member I at o.

Bincelightrayogisatananglewhichexceeds the critical angle for member I,it will not pass onthroughfaceabutwillbereflected atoto as y 0::-

amount of light received by photoelectric cell 6 Y may beyaried as thereflected beam of light is displaced when ice forms upon face a of mem-Our invention may be utilized to control the operation of any suitableice removal means. For purposesiof illustration only, such may comprisea plurality of resistors 8 which are arranged photocell i and, since theelectrical resistance of photocell I is Proportional to the amount oflight received on the elements thereof, a predetermined current willfiow therethrough in a circuit including the power supply It andresistor Ii. The amount of this current flowing through resistor II willobviously determine the bias" on grid Ilb of the amplifier II. Thevalues'of the component parts of the said grid circuit are soproportioned that when the reflected light my on strikes upon photocell8, grid Il'b is of sue a bias that the current flowing from filament Into plate Iflc and thence through the energizing coil for relay I2 andindicator II is insufiicient to cause either relay I! to close itscontacts Ila or an indication to be given by the indicating member ofindicator II.

Should. however, a coating of ice I! build up upon the surface ofairfoil 2 and face a of light pervious member I, the ray of light 0 willno longer be reflected at 0. Since the critical angle as between glassand water is approximately the rayoflightogwillpassinto the coatingofice It, becoming ray co, and being refracted slightly upon entry becauseof the difference in their indices of refraction. 1f the angle of ray.

00' with respect to a normal at the surface of the ice coating through0' exceeds 48 38', this being the critical angle as between ice and air,ray 00 will not pass into the air but will be reflected at Ray 00" willnot now impinge upon the light sensitive elements of photocell 6, sinceit will have been displaced beyond theaperture8incasingl.1f,ontheotherhand,the angle of ray 00' with respectto a normal through pointo' islessthan48 36',rayoo' willnotbe reflectedbut will pass intothe air being refracted at o'. In either eventphotocell i will no longer receive light from source 8 and itsresistance to current flow therethrough is therefore increased,

causing a decrease in the amount of current flowing through resistor IIand hence producing a change in the bias of grid Ilb of amplifier II.Thischangeinbiasof amplifier Ilissufncientto materially increase thecurrent flow in the plate our apparatus, photocell 8 may be connected incircuit thereof which includes the winding of relay I2 and indicator II,and such increase is sufficient to cause the contacts Ila of relay II toclose and the indicating element of indicator II to operate. v

When contacts Ila are thus closed, a circuit will be completed from thepower source It to the resistor heater units I.

When the coating of ice has been melted by the heat from the gle-icerheating units I, the beam of light from source 8 again will be re-.fiected at point 0 on face a of member I, and its reflection will againimp e upon the elements of photocell 6, thus restoring the bias of thegrid lllb of amplifier II to'its original value. The

subsequent reduction in current flow through the plate circuit ofamplifier II will then be insufficlentto keep the contacts I2a of relayI! closed,

EXAMINER thus breaking the circuit from power source It to the resistorheating units I.

Likewise, the reduction in current flow in the plate circuit ofamplifier II will also cause the indicating element of indicator II tomove back to its initial position.

As hereinbefore stated in the introduction to the description of theillustrated embodiment, our invention may be applied to any surface uponwhich ice may form and is not to be limited to any specific application.If desired. the appsassarsr 3 light pervious member is free from ice,and conratus may be utilized with the indicator I i alone,

in which case the operator could manually turn on the de-icing mechanismwhen the indicator showed that ice was forming. Or the apparatus may bemade entirely automatic and the indicator eliminatedjif desired.Likewise, certain other changes and modifications in the particularapparatus shown and described will occur toandmaybemadebythoseskilledintheart without departing from the spirit andscope of our invention. I

For example, the photoelectric cell may be positioned to receive lightrays which are refracted ,through, rather than totally reflected from,a'

light pervious member, in which case a layer of ic as it is built upupon a face of the light pervi ous member would cause a shift in therefracted rays away from or into the cell I. This shift in the rayrelative to the photoelectric cell wouldthen cause a change in itselectrical conducting characteristics which would be effective tooperate an indicator or turn on-the de-icing mechationed so as to exposeat least a portion of one face thereof with an exposed surface subjectto icing, means for directing a beam of light into said light perviousmember at such an angle as willcausesaidbeamtobereflectedatthe exposedface portion thereof, a light sensitive device disposed to receive atleast a portion of said reflected light beam when exposed face portionof said .trolmeansresponshetoachangeinchgracteris tie in said lightsensitive device as said reflected light beam is displaced by formationof ice upon th exposed faceporfionofsaidlightpervimis member.

2. Apparatus of the class described comprising, a light pervious member,said member being positioned so as to expose at least a portion of oneface thereof with an exposed surface subject to icing, means fordirecting a beam of light into said light pervious member and at such anangle as will cause said beam to be reflected back into said member fromthe exposed face portion thereof, a photoelectric device disposed toreceive at least a part of the reflection from said light beam, a powersource, control means, and means connecting said control means and saidphotoelectric device in an electrical circuit to said source of power,said control means being operable in response to a change in current insaid circuit effected by a change in conductivity in said photoelectricdevice as said reflected light beam is displaced by the formation of acoating of ice upon the exposed face portion of said light perviousmember.

3. Apparatus of the class described comprising, i

a prism-like light pervious member having a critical angle less than 45,said member including two plane faces at right angles to each other anda third face the contour of which conforms substantially to the contourof ancxpo ed surface subject to icing, said lightpervious member beinpositioned so as to expose the said third face thereof with said exposedsurface, means for directing a beam of light into said light perviousmember normal to one of the plane faces thereof so that said light beamwill impinge upon and be reflected by the said third face thereof, aphotoelectric device disposed to receive said reflected light beam, apower source, control means, and means connecting said control means andsaid photoelectric device in an electrical circuit to said source ofpower, said control means being operable in response to a change incurrent in said circuit effected by a change in conductivity of saidphotoelectric device as said reflected light beam is displaced by theformation of a coating of ice upon the said third face of said lightpervious member.

JliELVlIl-E 1". PETERS.

JOHN P. BOSTON mar M. Tennis.

